Dell’s m-commerce home page loads in 6.48 seconds while Walmart.com’s loads in 3.24.

Dell Inc. shot up four positions to land in the top five of this week’s Keynote Mobile Commerce Performance Index, but Walmart.com continues to rule the roost at No. 1.

Dell came in at No. 5 on the index, provided exclusively to Internet Retailer by Keynote Systems Inc., a mobile and web performance management firm. It earned a score of 809 out of 1,000, with an average m-commerce site home page load time of 6.48 seconds and a success rate of 98.86%. Walmart.com, by comparison, earned a score of 977, with an average home page load time of 3.24 seconds and a success rate of 99.54%.

StrandBooks.com came in second with a score of 883, an average load time of 2.60 seconds and a success rate of 98.04%. BarnesandNoble.com Inc. came in third with a score of 860, an average load time of 4.67 seconds and a success rate of 98.70%. And Walgreen Co. came in fourth with a score of 855, an average load time of 5.78 seconds and a success rate of 99.13%.

The average score of the 15 retailers in the index was 756, down 10 points from last week. The average m-commerce site home page load time was 5.62 seconds and the success rate was 97.79%. Click here and select Keynote Mobile Commerce Performance Index to see complete results for all of the index’s merchants for the week beginning Oct 4.

If m-commerce site performance is slipping, as it did with the index average this week, retailers should consider a variety of factors. But one of the biggest factors within a retailer’s control is the design of mobile web pages.

“Other than upgrading the web server farm with newer and faster hardware, it’s easy to conclude that there are few other ways to improve a mobile site’s performance. In fact, web page content is just as important a factor,” says Herman Ng, mobile performance evangelist at Keynote Systems. “The number of objects—images, cascading style sheets, Javascript, etc.—on a page is especially important for mobile site performance because the content will be requested and downloaded over a wireless high-latency connection. Therefore, every request implies adding a small amount of performance overhead. Keeping the total number of objects on a page relatively low is one strategy to adopt.”

Keynote Systems measures 15 representative m-commerce sites for Internet Retailer. The sites include merchants in various categories and channels, and of various sizes, ranging from such giants as Best Buy Co. and Foot Locker Inc. to midsized retailers like Sunglass Hut and Toolfetch.com LLC.

Keynote repeatedly tests the sites in the index Monday through Friday from 8 a.m. through midnight Eastern time, emulating three different smartphones on three different wireless networks: the iPhone on AT&T, the BlackBerry Curve on Sprint and the Droid (which uses the Android operating system) on Verizon. Keynote combines a site’s load time and success rate, equally weighted, into a single score. Given both performance and availability are important, the score reflects the overall quality of the home page. A higher score indicates better performance; scores also reflect how close sites are to each other in overall quality. The index’s average score is the midpoint among all the sites’ scores.